Method for transferring developed image

ABSTRACT

A method and apparatus for transferring a developed electrostatic image from an image-bearing member to a medium such as copy paper in response to the evenly distributed field produced by a D.C. biased metallized fiber brush roller which contacts the copy paper to produce the transfer.

United States Patent [191 Krause et al.

[ Oct. 15, 1974 METHOD FOR TRANSFERRING DEVELOPED IMAGE [75] Inventors:K. A. Krause, Mountain View;

Yaqub Moradazeh, Saratoga, both of Calif.

[73] Assignee: International Business Machines Corporation, Armonk, NY.

[22] Filed: Aug. 10, 1972 [21] App]. No.: 279,428

Related U.S. Application Data [62] Division of Ser. No. 92,038, Nov, 23,1970, Pat. No.

[52] U.S. C1. 117/17.5, 96/1.4 [51] Int. Cl. G03g 13/16, 603g 15/16 [58]Field of Search 117/17.5; 96/1 R, 1 S, 96/1 D, 1.4; 118/637; 355/3, 17

[56] References Cited UNITED STATES PATENTS 2,901,374 8/1959 Gundlach118/637 POWER SUPPLY 2,959,153 11/1960 Hider 118/637 3,152,012 10/1964Schaffert 118/637 3,328,193 6/1967 Oliphant el al. 118/637 3,368,8942/1968 Matkan et al 118/637 3,551,146 12/1970 Gundlach 96/1,4 3,589,8956/1971 Ville 118/637 3,599,603 8/1971 Ralston et a1... 118/637 3,627,52312/1971 Shelffo 96/1.4

Primary ExaminerMichael Sofocleous Attorney, Agent, or FirmOtto Schmid,Jr.

3 Claims, 4 Drawing Figures mammal 5:214 3L841;892

\ POWER SUPPLY IIIIIIIIIIIIIIIIA "'I'I'IIIIIII'I' mrmmnmmln 28- POWER Ik a SUPPER 62 26' '14 METHOD FOR TRANSFERRING DEVELOPED IMAGE This is adivision of application Ser. No. 92,038 filed Nov. 23, 1970 now U.S.Pat. No. 3,691,993 issued Sept. 19, 1972.

BACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates to electrostatic image systems and more particularly to transferof a developed image from an image-bearing member to a suitable transfermedium such as copy paper.

2. Description of the Prior Art One prior art method and apparatus fortransferring a developed image to a copy sheet comprises a systemwherein a corona discharge device is utilized to produce a charge on theback of the copy sheet to attract the image toner from the image formingsurface to the sheet. However, any vibration of the corona wire or dirtaccumulation on the corona wire causes an uneven distribution ofionization and consequently causes uneven toner transfer which isobservable on the copy. The ef ficiency of the corona discharge deviceand hence the quality of the resultant image varies widely with changesin temperature and relative humidity. In addition, when high densityimages are present, toner transfer by corona transfer techniques israther inefficient. Another prior art method and apparatus fortransferring a developed image utilizes a conductive roller member and abias potential applied to the roller to produce the transfer of thedeveloped image to the copy sheet. This method and apparatus producessatisfactory results under certain circumstances; however, theefficiency of transfer is low under certain conditions. In addition,sparking and other image distorting phenomena may occur as the copysheet is separated from the image forming surface. It is therefore anobject of this invention to produce apparatus and method for transferinga developed image comprising electrostatic charged developer particlesfrom an image forming surface to a web of transfer material to produce ahigh transfer efficiency and also a consistent image, under widelyvarying environmental conditions.

SUMMARY OF THE INVENTION The apparatus comprises an image formingsurface which may be an insulator or a photoconductive surface. Anelectrostatic image is produced on the surface by known techniques andthe image is developed utilizing electrostatically charged developerparticles which are commonly known as toner. A web of transfer materialis provided adjacent to the image surface. A brush having conductivefibers is also mounted adjacent to the image surface and a constantpotential difference is produced between the image surface and the brushmember by means of a suitable power supply. Relative motion is producedbetween the brush and the image surface so that the tips of the brushfibers move the web of transfer material into intimate contact with theimage surface. The potential difference is operative to attract thetoner particles comprising the developed image to the web of transfermaterial and due to the constant force provided by the brush fibers,substantially all of the developer particles are transferred from theimage surface to the web of transfer material. The image is then fixedto the web of transfer material by any suitable technique.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of aneleetrophotographic apparatus embodying the present invention;

FIG. 2 is an enlarged view showing in greater detail the metallizedfiber embodiment of the transfer brush means for the apparatus shown inFIG. 1;

FIG. 3 is a partial cross section view along the lines 33 of FIG. 1;

FIG. 4 is a schematic view of an alternate embodiment of the apparatusembodying the invention wherein a flat transfer brush means is utilized.

DESCRIPTION OF PREFERRED EMBODIMENTS One example of a particularapparatus in which the subject invention is adapted for use is theelectrophotographic apparatus shown in FIG. 1. In this apparatus, arotatable drum 10 carries around its periphery an eleetrophotographicphotoconductive member 12 on which is directed an image which it isdesired to be reproduced on the paper sheet 14. The surface of thephotoconductor is uniformly charged to a predetermined polarity bycorona discharge device 16. A document having the image to be copied isplaced so that a suitable exposure means is operable to direct the imageto expose station 18 onto the surface of the photoconductor 12. Relativemotion is provided for the document at a speed synchronized with thesurface speed of drum 10 in a manner known in the art. Where thephotoconductive surface is illuminated by the image, the surface isdischarged leaving a charged pattern in a form of the image to becopied.

Thereafter, the drum passes a development station 20 at which atoner-carrier mixture 22 is cascaded across or otherwise brought incontact with the electrostatic image on the surface of thephotoconductor 12 r as is known in the art. The toner, having a chargeoppodeveloped electrostatic image by the rollers 24. A soft brush means26 having resilient conductive fibers is disposed beneath the paper atthe area of contact with the drum. Power supply 28 is coupled to producea unidirectional potential between brush'member 26 andthe conductivebacking of photoconductor 12. The potential has a polarity opposite thatof the toner, thereby attracting the toner to the copy paper. After thistransfer operation, the paper 14 is separated from the drum and fed pasta fusing station (not shown) which serves to fuse and permanently fixthe toner to the paper. Since transfer of all the image toner 29 is notusually accomplished, residual toner 30 usually remains on the drumsurface after a transfer operation. The drum continues to rotate past acleaning apparatus 32 which cleans the surface of the photoconductor andremoves any excess toner. This operation completes the cycling of thedrum for reproducing the desired image.

The brush member 26 comprises a plurality of uni tary fibers 25 whichare permanently attached to the base member 27. The fibers extendsubstantially outward from the base and the fibers are of substantiallyuniform length so that a potential applied to the brush will produce asubstantially uniformly distributed field. The fibers may comprise anysuitable material such as metal fibers or non-metallic fibers which areprovided with a conductive coating. The thickness of the individualfibers is small so that a substantially constant force can be exerted bythe brush fibers on the transfer web so that intimate contact with theimage surface can be produced without regard to the density of thedeveloper particles in different portions of the developed image. Thefibers are preferably of a thickness approximating the size of theindividual toner particles so that the image transfer can beaccomplished without distortion of the image. This size fiber alsoeliminates damage to the image forming surface and to the copy sheetwhich would result from the use of thicker and stiffer brush fibers. Onesuitable material is stainless steel fibers approximately 12 microns indiameter which are woven into a plush fabric which is then attached to asuitable support member. This type of brush produces excellent transfer,but is difficult to manufacture with all fibers upstanding so that auniform field and-a uniform force are produced by the brush.

Another suitable type of brush (See FIG. 2) which is easily manufacturedand produces excellent operation is a brush comprising a nonconductivefiber to which a conductive coating is applied. Brushes of syntheticmaterials such as dynel and rayon can be manufactured with uniformlydistributed upstanding fibers on a base material. The fibers are coatedwith a conductive material by any suitable means to provide the desiredconductivity of the fibers. In the embodiment shown in FIG. 2 of thedrawings, brush means 26' comprises a base member 38 to which is fixed aplurality of uniform upstanding fibers. The fibers comprise an innernonconductive part 40 which has an outer conductive coating 42. Thisconstruction gives control over the conductivity of the fibers so thatan effective technique for the prevention of arcing during separation ofthe image surface and the transfer material is produced.

One suitable technique for coating the surface of the fibers is thetechnique known in the art as electroless plating. One example of abrush construction utilizing this technique comprises a rayon plushfabric since this material contains a combination of physical, chemicaland electrostatic properties which are suitable for this use. Othertypes of knit or construction such as sliver knit or flocking may beused for this purpose which results in plush fabrics with upstanding orsubstantially upstanding fibers. The particular fabric utilizes a doubleshuttle type of weave which is essential in keeping the fibersseparated. The fibers are first washed and then sensitized by immersionin a suitable sensitizing solution such as stannous chloride. Aftersufficient rinsing, the fabric is then activated utilizing a suitableactivating solution, for example, immersion in acidic palladium chloridesolutions. After suitable rinsing, the material is placed in a properplating bath such as a copper plating bath for a time which varies withthe type of bath and the desired conductivity to be produced in thefibers. The material is then rinsed and dried. This operation produces asuitable conductive coating on the fibers so that a brush is produced byfixing the fabric to a suitable support member to produce the transferbrush. Other types of conductive coating may be produced on the fibersurface using electroless plating, for

example, nickel, cobalt, iron, etc. In these cases a trace of phosphorususually codeposits with the metallic layer. Precious metals such asgold, platinum and rhodium can be deposited by a double platingtechnique in which copper is first deposited on the synthetic fiber bythe electroless plating method followed by an immersion platingtechnique in which all or part of copper film is converted to thedesired precious metallic film. For this purpose an acidic salt solutionof precious metal is employed in which the copper plated fabric isimmersed, then rinsed and dried.

Relative motion may be produced between the image forming surface andthe brush means 26 by any suitable means. In the embodiment shown, drum10 is rotated about its axis from a suitable drive motor 34 by suitablebelts or gears (shown dotted in the drawings). If desired, brush means26 may also be rotated. Brush 26 may be rotated at a speed synchronizedwith the drum speed or driven at a faster rate to lessen the adverseeffect in the event of any separation or bunching of the fibers in brush26. The flat brush 26" shown in FIG. 4 is maintained stationary andreliable transfer of the image is produced.

Brush 26 should maintain at least a minimum area of contact to providegood transfer. A particular apparatus utilized a flat image formingsurface and a 2 Vs inch diameter transfer brush. The brush was mohairwith electroless plated copper fibers about one-eighth of an inch long.A range of potentials (7001,200) and brush compressions were tried andthe optimum configuration for this apparatus was found to be a potentialof 1,100 volts with about 2mm compression in the brush fibers whichproduced a contact area approximately one inch wide. A 2 As inchdiameter stainless steel fiber brush with /s inch fibers was alsoutilized. The optimum transfer current which produced good transferwithout arcing was found to be O.2p.A/in A series resistor was used withthe stainless steel fiber brush to limit the current to this level.

The invention is also applicable to other types of image producingsystems other than the embodiment shown in the drawings. For example, ina system with a dielectric image bearing surface, a higher transferpotential was found to be more suitable. Potentials in the range of1,000 to 2,000 volts were found suitable for good transfer in apparatusof this type.

While the invention has been particularly shown and described withreference to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in the form and detailsmay be made therein without departing from the spirit and scope of theinvention.

We claim:

1. The method of transferring a developed image comprisingelectrostatically charged developer particles from an image formingsurface to a web of transfer material comprising the steps of:

forming a developed image on an image forming surface;

placing over the developed image a web of transfer material;

rotating a brush means comprising a plurality of conductive fibers;

producing a constant potential difference between said brush means andsaid image forming surface; and

producing relative motion between the brush means and the image formingsurface so that the tips of the fibers move the web of transfer materialinto abutting contact with said image forming surface whereby saidpotential is operative to transfer the developed image to said web oftransfer material.

producing a constant potential difference between said brush means andsaid image forming surface; and

producing relative motion between the brush means and the image formingsurface so that the tips of the fibers move the web of transfer materialinto abutting contact with said image forming surface whereby saidpotential is operative to transfer the developed image to said web oftransfer material.

- 3. The method according to claim 2 wherein said non-conductive fiberscomprise synthetic material.

1. THE METHOD OF TRANSFERRING A DEVELOPED IMAGE COMPRISINGELECTROSTATICALLY CHARGED DEVELOPER PARTICLES FROM AN IMAGE FORMINGSURFACE TO A WEB OF TRANSFER MATERIAL COMPRISING THE STEPS OF: FORMING ADEVELOPED IMAGE ON AN IMAGE FORMING SURFACE, PLACING OVER THE DEVELOPEDIMAGE A WEB OF TRANSFER MATERIAL, ROTATING A BRUSH MEANS COMPRISING APLURALITY OF CONDUCTIVE FIBERS, PRODUCING A CONSTANT POTENTIALDEFFERENCE BETWEEN SAID BRUSH MEANS AND SAID IMAGE FORMING SURFACE, ANDPRODUCING RELATIVE MOTION BETWEEN THE BRUSH OEANS AND THE IMAGE FORMINGSURFACE SO THAT THE TIPS OF THE FIBERS MOVE THE WEB OF TRANSFER MATERIALINTO ABUTTING CONTACT WITH SAID IMAGE FORMING SURFACE WHEREBY SAIDPOTENTIAL IS OPERATIVE TO TRANSFER THE DEVELOPED IMAGE TO SAID WEB OFTRANSFER MATERIAL.
 2. The method of transferring a developed imagecomprising electrostatically charged developer particles from an imageforming surface to a web of transfer material comprising the steps of:forming a developed image on an image forming surface; placing over thedeveloped image a web of transfer material; rotating a brush meanscomprising a plurality of fibers, said fibers comprising non-conductivefibers having a conductive coating thereon; producing a constantpotential difference between said brush means and said image formingsurface; and producing relative motion between the brush means and theimage forming surface so that the tips of the fibers move the web oftransfer material into abutting contact with said image forming surfacewhereby said potential is operative to transfer the developed image tosaid web of transfer material.
 3. The method according to claim 2wherein said non-conductive fibers comprise synthetic material.